Search

We present optical observations of supernova (SN) 2014ek, discovered during the Tsinghua University–National Astronomical Observatories, Chinese Academy of Sciences (NAOC) Transient Survey (TNTS), which shows properties that are consistent with those of SN 2002cx-like events (dubbed as SNe Iax). The photometry indicates that it is underluminous compared with normal SNe Ia, with the absolute V -band peak magnitude being −17.66 ± 0.20 mag. The spectra are characterized by highly ionized Fe iii and intermediate-mass elements (IMEs). The expansion velocity of the ejecta is found to be ∼5000 km s−1 near the maximum light, only half of that measured for normal SNe Ia. The overall spectral evolution is quite similar to that of SN 2002cx and SN 2005hk, while the absorption features of the main IMEs seem to be relatively weaker. The 56Ni mass synthesized in the explosion is estimated to be about 0.08 M⊙ from the pseudo-bolometric light curve. Based on a large sample of SNe Iax, we examined the relations between peak luminosity, ejecta velocity, decline rate and peak V  −  R colour, but did not find noticeable correlations between these observables, in particular when a few extreme events like SN 2008ha are excluded from the analysis. For this sample, we also studied the birthplace environments and confirm that they still hold the trend of occurring preferentially in late-type spiral galaxies. Moreover, SNe Iax tend to occur in large star-forming regions of their host galaxies, more similar to SNe Ibc than SNe II, favouring the idea that their progenitors should be associated with very young stellar populations. Nevertheless, the progenitors of SNe Iax may have relatively lower metallicity, as suggested by the evidence that they prefer to explode in outer regions of host galaxies. [ABSTRACT FROM AUTHOR]

An exact calculation of CaI λ6439 Å absorption profiles in the spectra of optical stars in low-mass X-ray binary systems is carried out. The calculations are used to revise a formula relating the rotational broadening of lines and the component-mass ratio. In the case of modest (substantial) X-ray heating, failure to take into account the tidal-rotational deformation of the figure of the star leads to overestimation (underestimation) of the mass of the relativistic object. The radial-velocity curves of optical stars are modeled for binary systems with various parameters and X-ray heating powers k; corresponding tables of K corrections are presented. Refined values for the component-mass ratio q = 23 ± 1, black-hole mass M = 8.4 ± 0.5, and optical-star mass M = 0.36 ± 0.07 for the GS 2023+338 (V404 Cyg) system are presented. [ABSTRACT FROM AUTHOR]

The element abundance ratios of four low-mass stars with extremely low metallicities (abundances of elements heavier than helium) indicate that the gas out of which the stars formed was enriched in each case by at most a few-and potentially only one-low-energy supernova. Such supernovae yield large quantities of light elements such as carbon but very little iron. The dominance of low-energy supernovae seems surprising, because it had been expected that the first stars were extremely massive, and that they disintegrated in pair-instability explosions that would rapidly enrich galaxies in iron. What has remained unclear is the yield of iron from the first supernovae, because hitherto no star has been unambiguously interpreted as encapsulating the yield of a single supernova. Here we report the optical spectrum of SMSS J031300.36−670839.3, which shows no evidence of iron (with an upper limit of 10−7.1 times solar abundance). Based on a comparison of its abundance pattern with those of models, we conclude that the star was seeded with material from a single supernova with an original mass about 60 times that of the Sun (and that the supernova left behind a black hole). Taken together with the four previously mentioned low-metallicity stars, we conclude that low-energy supernovae were common in the early Universe, and that such supernovae yielded light-element enrichment with insignificant iron. Reduced stellar feedback both chemically and mechanically from low-energy supernovae would have enabled first-generation stars to form over an extended period. We speculate that such stars may perhaps have had an important role in the epoch of cosmic reionization and the chemical evolution of early galaxies. [ABSTRACT FROM AUTHOR]

We study disparity between H α and H β in early spectra of the type IIP supernova SN 2008in. The point is that these lines cannot be described simultaneously in a spherically-symmetric model with the smooth density distribution. It is shown that an assumption of a clumpy structure of external layers of the envelope resolves the problem. We obtain estimates of the velocity at the inner border of the inhomogeneous zone (≈6100 km s), the filing factor of inhomogeneities (≤0.5), and the mass of the inhomogeneous layers (∼0.03 M). The amplitude of flux fluctuations in the early spectrum of H α (Δ F/F ∼ 10) imposes a constraint on the size of inhomogeneities (≤200 km s). A detection of fluctuations in the early H α of type IIP supernovae might become an observational test of the inhomogeneous structure of their envelopes. We propose also the indirect test of the clumpy structure of external layers: the study of properties of the initial radiation outburst due to the shock breakout. The inhomogeneous structure of external layers of type IIP supernovae could be an outcome of density perturbations and density inversion in outer convective layers of presupernova red supergiant. [ABSTRACT FROM AUTHOR]

Ultraluminous X-ray sources (ULXs) are some of the brightest phenomena found outside of a galaxy's nucleus, and their explanation typically invokes accretion of material onto a black hole. Here, we perform the largest population study to date of ULXs in early-type galaxies, focusing on whether a galaxy's large-scale environment can affect its ULX content. Using the AMUSE survey, which includes homogeneous X-ray coverage of 100 elliptical galaxies in the Virgo cluster and a similar number of elliptical galaxies in the field (spanning stellar masses of 108-1012M☼), we identify 37.9 ± 10.1 ULXs in Virgo and 28.1 ± 8.7 ULXs in the field. Across both samples, we constrain the number of ULXs per unit stellar mass, i.e., the ULX specific frequency, to be 0.062 ± 0.013 ULXs per 1010M☼ (or about 1 ULX per 1.6 × 1011M☼ of galaxy stellar mass). We find that the number of ULXs, the specific frequency of ULXs, and the average ULX spectral properties are all similar in both cluster and field environments. Contrary to late-type galaxies, we do not see any trend between specific ULX frequency and host galaxy stellar mass, and we show that dwarf ellipticals host fewer ULXs than later-type dwarf galaxies at a statistically meaningful level. Our results are consistent with ULXs in early-type galaxies probing the luminous tail of the low-mass X-ray binary population, and are briefly discussed in context of the influence of gravitational interactions on the long-term evolution of a galaxy's (older) stellar population. [ABSTRACT FROM AUTHOR]

Using a sample of 608 Type Ia supernovae from the SDSS-II and BOSS surveys, combined with a sample of foreground galaxies from SDSS-II, we estimate the weak lensing convergence for each supernova line of sight. We find that the correlation between this measurement and the Hubble residuals is consistent with the prediction from lensing (at a significance of 1.7σ). Strong correlations are also found between the residuals and supernova nuisance parameters after a linear correction is applied. When these other correlations are taken into account, the lensing signal is detected at 1.4σ. We show, for the first time, that distance estimates from supernovae can be improved when lensing is incorporated, by including a new parameter in the SALT2 methodology for determining distance moduli. The recovered value of the new parameter is consistent with the lensing prediction. Using cosmic microwave background data from WMAP7, H0 data from Hubble Space Telescope and Sloan Digital Sky Survey (SDSS) Baryon acoustic oscillations measurements, we find the best-fit value of the new lensing parameter and show that the central values and uncertainties on Ωm and w are unaffected. The lensing of supernovae, while only seen at marginal significance in this low-redshift sample, will be of vital importance for the next generation of surveys, such as DES and LSST, which will be systematics-dominated. [ABSTRACT FROM AUTHOR]

We report results from TeV gamma-ray observations of the microquasar Cygnus X-3. The observations were made with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) over a time period from 2007 June 11 to 2011 November 28. VERITAS is most sensitive to gamma rays at energies between 85 GeV and 30 TeV. The effective exposure time amounts to a total of about 44 hr, with the observations covering six distinct radio/X-ray states of the object. No significant TeV gamma-ray emission was detected in any of the states, nor with all observations combined. The lack of a positive signal, especially in the states where GeV gamma rays were detected, places constraints on TeV gamma-ray production in Cygnus X-3. We discuss the implications of the results. [ABSTRACT FROM AUTHOR]

The progenitors of Type IIP supernovae (SNe) have an apparent upper limit to their initial masses of about 20 M☉, suggesting that the most massive red supergiants evolve to warmer temperatures before their terminal explosion. But very few post-red supergiants are known. We have identified a small group of luminous stars in M31 and M33 that are candidates for post-red supergiant evolution. These stars have A-F-type supergiant absorption line spectra and strong hydrogen emission. Their spectra are also distinguished by the Ca ii triplet and [Ca ii] doublet in emission formed in a low-density circumstellar environment. They all have significant near- and mid-infrared excess radiation due to free-free emission and thermal emission from dust. We estimate the amount of mass they have shed and discuss their wind parameters and mass loss rates, which range from a few × 10-6 to 10-4 M☉ yr-1. On an H-R diagram, these stars will overlap the region of the luminous blue variables (LBVs) at maximum light; however, the warm hypergiants are not LBVs. Their non-spherical winds are not optically thick, and they have not exhibited any significant variability. We suggest, however, that the warm hypergiants may be the progenitors of the "less luminous" LBVs such as R71 and even SN1987A. [ABSTRACT FROM AUTHOR]

Type II supernovae (SNe) can be used as a star formation tracer to probe the metallicity distribution of global low-redshift star formation. We present oxygen and iron abundance distributions of Type II SN progenitor regions that avoid many previous sources of bias. Because iron abundance, rather than oxygen abundance, is of key importance for the late stage evolution of the massive stars that are the progenitors of core-collapse supernovae, and because iron enrichment lags oxygen enrichment, we find a general conversion from oxygen abundance to iron abundance. The distributions we present here are the best yet observational standard of comparison for evaluating how different classes of supernovae depend on progenitor metallicity. We spectroscopically measure the gas-phase oxygen abundance near a representative subsample of the hosts of Type II SNe from the first-year Palomar Transient Factory (PTF) SN search, using a combination of Sloan Digital Sky Survey (SDSS) spectra near the SN location (9 hosts) and new longslit spectroscopy (25 hosts). The median metallicity of these 34 hosts at or near the SN location is 12+log(O/H) = 8.65, with a median error of 0.09. The median host galaxy stellar mass from fits to SDSS photometry is 109.9M_. They do not show a systematic offset in metallicity or mass from a redshift-matched sample of the MPA/JHU value-added catalog. In contrast to previous SN host metallicity studies, this sample is drawn from a single survey. It is also drawn from an areal rather than a targeted survey, so SNe in the lowest-mass galaxies are not systematically excluded. Indeed, the PTF SN search has a slight bias toward following up transients in low mass galaxies. The progenitor region metallicity distribution we find is statistically indistinguishable from the metallicity distribution of Type II SN hosts found by targeted surveys and by samples from multiple surveys with different selection functions. Using the relationship between iron and oxygen abundances found for Milky Way disk, bulge, and halo stars, we translate our distribution of Type II SN environments as a function of oxygen abundance into an estimate of the iron abundance, since iron varies more steeply than oxygen. We find that though this sample spans only 0.65 dex in oxygen abundance, the gap between the iron and oxygen abundance is 50% wider at the low-metallicity end of our sample than at the high-metallicity end. [ABSTRACT FROM AUTHOR]

Context. M17 is one of the best studied giant HII regions in our galactic neighborhood. It should also provide a suitable environment for the class of fully ionized jets externally irradiated by the presence of nearby hot stars. However, no such jets have been observed thus far in M17. Aims. We report on a visible imaging survey of the M17 nebula with the goal of identifying likely shock-excited nebulosities. Methods. We imaged M17 through narrow-band filters centered on the most intense visible lines of [OIII], Hα+[NII], [SII], and Hα. We obtained follow-up spectroscopy of the only jet-like structure identified in the images.We also used published X-ray observations of M17 obtained with the Chandra X-ray Observatory, as well as infrared data obtained with the Very Large Telescope and with the Spitzer Space Telescope, to look for evidence of a jet-driving source. Results. We have detected what appears to be the first jet identified in M17 visible HII region. The jet is composed of a set of knots, two of which have significant radial velocities with respect to the HII region, and a distant arc-like bright nebulosity that may represent an early episode of intense mass loss by the jet-driving source. The follow-up spectra of the structures composing the jet, including the arc, support this interpretation by revealing intense forbidden lines of [NII] and [SII] due to enhanced collisional excitation in shocks. The presence of a X-ray source, most likely a young stellar object, at a position where the jet launching source should be expected to lie reinforces the interpretation. We identify a tentative near-infrared counterpart of the X-ray source, although it is offset by 1: 009 from the nominal position of the X-ray source, which is almost three times the radius of its positional uncertainty. The very weak [OI] emission in the spectra of the jet knots and the arc suggests that they are nearly fully ionized, in agreement with the environment in which the jet is propagating. [ABSTRACT FROM AUTHOR]

ABSTRACT The X-ray variations of hard state black hole X-ray binaries above 2 keV show 'hard lags', in that the variations at harder energies follow variations at softer energies, with a time lag τ depending on frequency ν approximately as τ∝ν−0.7. Several models have so far been proposed to explain this time delay, including fluctuations propagating through an accretion flow, spectral variations during coronal flares, Comptonization in the extended hot corona or a jet, or time delays due to large-scale reflection from the accretion disc. In principle, these models can be used to predict the shape of the energy spectrum as well as the frequency dependence of the time lags, through the construction of energy-dependent response functions which map the emission as a function of time delay in the system. Here we use this approach to test a simple reflection model for the frequency-dependent lags seen in the hard state of GX 339−4, by simultaneously fitting the model to the frequency-dependent lags and energy spectrum measured by XMM-Newton in 2004 and 2009. Our model cannot simultaneously fit both the lag and spectral data, since the relatively large lags require an extremely flared disc which subtends a large solid angle to the continuum at large radii, in disagreement with the observed Fe Kα emission. Therefore, we consider it more likely that the lags >2 keV are caused by propagation effects in the accretion flow, possibly related to the accretion disc fluctuations which have been observed previously. [ABSTRACT FROM AUTHOR]

ABSTRACT Pristine stars with masses between ∼140 and 260 M⊙ are theoretically predicted to die as pair-instability supernovae. These very massive progenitors could come from Population III (Pop III) stars in the early universe. We model the light curves and spectra of pair-instability supernovae over a range of masses and envelope structures. At redshifts of reionization z≥ 6, we calculate the rates and detectability of pair-instability and core-collapse supernovae, and show that with the James Webb Space Telescope it is possible to determine the contribution of Pop III and Pop II stars towards reionization by constraining the stellar initial mass function at that epoch using these supernovae. We also find the rates of Type Ia supernovae, and show that they are not rare during reionization, and can be used to probe the mass function at 4-8 M⊙. If the budget of ionizing photons was dominated by contributions from top-heavy Pop III stars, we predict that the bright end of the galaxy luminosity function will be contaminated by pair-instability supernovae. [ABSTRACT FROM AUTHOR]

We present surprising similarities between some bipolar planetary nebulae (PNe) and eruptive objects with peak luminosity between novae and supernovae. The latter group is termed ILOT for intermediate-luminosity optical transients (other terms are intermediate-luminosity red transients and red novae). In particular, we compare the PN, NGC 6302 and the pre-PNe OH231.8+4.2, M1-92, and IRAS 22036+5306 with the ILOT NGC 300 OT2008-1. These similarities lead us to propose that the lobes of some (but not all) PNe and pre-PNe were formed in an ILOT event (or several close sub-events). We suggest that in both types of objects the several months long outbursts are powered by mass accretion onto a main-sequence (MS) companion from an asymptotic giant branch (AGB, or extreme-AGB) star. Jets launched by an accretion disk around the MS companion shape the bipolar lobes. Some of the predictions that result from our comparison is that the ejecta of some ILOTs will have morphologies similar to those of bipolar PNe, and that the central stars of the PNe that were shaped by ILOTs should have an MS binary companion with an eccentric orbit of several years long period. [ABSTRACT FROM AUTHOR]

We investigate a sample of 11 Galactic X-ray sources recently discovered with INTEGRAL or RXTE with the goal of identifying their optical and/or near-infrared (NIR) counterpart. For this purpose, new Chandra positions of nine objects are presented together with follow-up observations of all the targets in the optical and NIR. For the four sources IGR J16194−2810, IGR J16479−4514, IGR J16500−3307 and IGR J19308+0530, the Chandra position confirms an existing association with an optical/NIR object, while for two sources, XTE J1716−389 and IGR J18490−0000, it rules out previously proposed counterparts indicating new ones. In the case of IGR J17597−220, a counterpart is selected out of the several possibilities proposed in the literature, and we present the first association with an optical/NIR source for IGR J16293−4603 and XTE J1743−363. Moreover, optical/NIR observations are reported for XTE J1710−281 and IGR J17254−3257; we investigate the counterpart to the X-ray sources based on their XMM-Newton positions. We discuss the nature of each system considering its optical/NIR and X-ray properties. [ABSTRACT FROM AUTHOR]

We analyse the colour gradients (CGs) of nearby Sloan Digital Sky Survey galaxies estimated by their photometrical parameters (Sérsic index, total magnitude and effective radius). From synthetic spectral models based on a simplified star formation recipe, we derive the mean spectral properties and explain the observed radial trends of the colour as gradients of the stellar population age and metallicity. CGs have been correlated with colour, luminosity, size, velocity dispersion and stellar mass. Distinct behaviours are found for early- and late-type galaxies (ETGs and LTGs), pointing to slightly different physical processes at work in different morphological types and at different mass scales. In particular, the most massive ETGs ( ) have shallow (even flat) CGs in correspondence of shallow (negative) metallicity gradients. In the stellar mass range ( , the metallicity gradients reach their minimum of . At , colour and metallicity gradient slopes suddenly change. They turn out to anticorrelate with the mass, becoming highly positive at the very low masses, the transition from negative to positive occurring at . These correlations are mirrored by similar trends of CGs with the effective radius and the velocity dispersion. We have also found that age gradients anticorrelate with metallicity gradients, as predicted by hierarchical cosmological simulations for ETGs. On the other side, LTGs have colour and metallicity gradients which systematically decrease with mass (and are always more negative than in ETGs), consistently with the expectation from gas infall and supernovae feedback scenarios. Metallicity is found to be the main driver of the trend of CGs, especially for LTGs, but age gradients are not negligible and seem to play a significant role too. Owing to the large data set, we have been able to highlight that older galaxies have systematically shallower age and metallicity gradients than younger ones. The emerging picture is qualitatively consistent with the predictions from hydrodynamical and chemodynamical simulations. In particular, our results for high-mass galaxies are in perfect agreement with predictions based on the merging scenario, while the evolution of LTGs and younger and less massive ETGs seems to be mainly driven by infall and supernovae feedback. [ABSTRACT FROM AUTHOR]

We perform a statistical analysis of the properties of 170 rich clusters of galaxies. We confirm the existence of correlations between the X-ray luminosity and temperature of the cluster intergalactic medium (IGM) and between the velocity dispersion of the galaxies and the X-ray luminosity of the IGM. In addition, we have found a new anti-correlation between the optical luminosity in H α and the X-ray luminosity of the cluster IGM: log $$ \left( {\frac{{L_{H\alpha } }} {{L_ \odot }}} \right) = a - b\log \left( {\frac{{L_x }} {{L_ \odot }}} \right) $$. Clusters form sequences with different values of a but similar values of b. [ABSTRACT FROM AUTHOR]

The Cartwheel galaxy harbours more ultraluminous X-ray sources (ULXs) than any other galaxy observed so far, and as such it is a particularly interesting target to study them. In this paper, we analyse the three Chandra observations of the brightest ULX (N10) in the Cartwheel galaxy, in light of current theoretical models suggested to explain such still elusive objects. For each model, we derive the relevant spectral parameters. Based on self-consistency arguments, we can interpret N10 as an accreting binary system powered by an black hole. A young supernova strongly interacting with its surroundings is a likely alternative that can be discarded only with the evidence of a flux increase from future observations. [ABSTRACT FROM AUTHOR]

We examined the variability of three ultraluminous X-ray sources (ULXs) in the 2003, 110 ks XMM–Newton observation of NGC 253. Remarkably, we discovered ULX1 to be three times more variable than ULX2 in the 0.3–10 keV band, even though ULX2 is brighter. Indeed, ULX1 exhibits a power density spectrum that is consistent with the canonical high state or very high/steep power-law states, but not the canonical low state. The 0.3–10 keV emission of ULX1 is predominantly non-thermal, and may be related to the very high state. We also fitted the ULX spectra with disc blackbody, slim disc and convolution Comptonization (simpl⊗diskbb) models. The brightest ULX spectra are usually described by two emission components (disc blackbody + Comptonized component); however, thesimpl model results in a single emission component, and may help determine whether the well-known soft excess is a feature of ULX spectra or an artefact of the two-component model. Thesimpl models were rejected for ULX3 (and also for the black hole + Wolf–Rayet binary IC10 X-1); hence, we infer that the observed soft-excesses are genuine features of ULX emission spectra. We use an extended corona scenario to explain the soft excess seen in all the highest quality ULX spectra, and provide a mechanism for stellar mass black holes to exhibit super-Eddington luminosities while remaining locally sub-Eddington. [ABSTRACT FROM AUTHOR]

Globular clusters and x-ray astronomy have a long and fruitful history. Uhuru and 050-7 revealed highly luminous (>1036 ergs-1) x-ray sources in globular clusters, and Einstein and ROSATrevealed a larger population of low-luminosity (<1033 ergs-1) x-ray sources. It was realized early on that the high-luminosity sources were low-mass x-ray binaries in outburst and that they were orders of magnitude more abundant per unit mass in globular clusters than in the rest of the galaxy. However, the low-luminosity sources proved difficult to classify. Many ideas were put forth-low-mass x-ray binaries in quiescence (qLMXBs). cataclysmic variables (CVs), active main-sequence binaries (ABs), and millisecond pulsars (MSPs)-but secure identifications were scarce. In R0SATobservations of 55 clusters, about 25 low-luminosity sources were found. Chandra has now observed over 80 Galactic globular clusters, and these observations have revealed over 1,500 x-ray sources. The superb angular resolution has allowed for many counterpart identifications, providing clues to the nature of this population. It is a heterogeneous mix of qLMXBs, (Vs. AB5, and MSPs, and it has been shown that the qLMXBs and (Vs are both, in part, overabundant like the luminous LMXBs. The number of x-ray sources in a cluster correlates very well with its encounter frequency. This points to dynamical formation scenarios for the x-ray sources and shows them to be excellent tracers of the complicated internal dynamics. The relation between the encounter frequency and the number of x-ray sources has been used to suggest that we have misunderstood the dynamical states of globular clusters. [ABSTRACT FROM AUTHOR]

For almost two decades the properties of ‘dwarf’ galaxies have challenged the cold dark matter (CDM) model of galaxy formation. Most observed dwarf galaxies consist of a rotating stellar disk embedded in a massive dark-matter halo with a near-constant-density core. Models based on the dominance of CDM, however, invariably form galaxies with dense spheroidal stellar bulges and steep central dark-matter profiles, because low-angular-momentum baryons and dark matter sink to the centres of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet reconciled theory with observations of present-day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different dark-matter particle candidate. Here we report hydrodynamical simulations (in a framework assuming the presence of CDM and a cosmological constant) in which the inhomogeneous interstellar medium is resolved. Strong outflows from supernovae remove low-angular-momentum gas, which inhibits the formation of bulges and decreases the dark-matter density to less than half of what it would otherwise be within the central kiloparsec. The analogues of dwarf galaxies—bulgeless and with shallow central dark-matter profiles—arise naturally in these simulations. [ABSTRACT FROM AUTHOR]

The single-degenerate model is the most widely accepted progenitor model of Type Ia supernovae (SNe Ia), where a carbon–oxygen white dwarf (CO WD) accretes hydrogen-rich material from its companion to increase its mass. The companion may be a main-sequence (MS) star or a subgiant star (WD + MS). When the CO WD approaches the Chandrasekhar mass limit, it explodes as a SN Ia and part of the supernova ejecta collides into the companion envelope. After the impact of the ejecta, the companion survives and may show some special properties. A good way to verify the single-degenerate model is to study the interaction between the supernova ejecta and the companion, and/or search for the companion in the remnant of a SN Ia. Following previous studies, we have carried out a series of binary population synthesis studies exploring the properties of the companions of SNe Ia for different metallicities Z. We present the distributions of the masses , radii of the companions, periods PSN and ratios of separations to radii of WD + MS systems for various Z at the moment of supernova explosion. These parameters can be applied to constrain the numerical simulation of the interaction between the ejecta of a supernova and its companion. We also show the distributions of some integral properties of the companions, i.e. the mass, the space velocity and the surface gravity, for various Z after the interaction. The distributions may help us to search for the companion in a supernova remnant. All the parameters above change significantly with Z. Incorporating the simulation results of the interaction between supernova ejecta and companions from other works into our binary population synthesis study, we found that more than 75 per cent of all supernovae have a strong enough polarization signal to be detected by spectropolarimetric observations. We also found that 13–14 per cent of SNe Ia belong to the class of supernovae like 1991T, which is consistent with observations within the errors. This may indicate that 1991T-like SNe do not have any special physical properties except for the viewing angle of the observer. [ABSTRACT FROM AUTHOR]

We investigate the far-infrared (FIR) properties of X-ray sources detected in the Chandra Deep Field-South (CDF-S) survey using the ultradeep 70 and 24 μm Spitzer observations taken in this field. Since only 30 (i.e. ≈10 per cent) of the 266 X-ray sources in the region of the 70 μm observations are detected at 70 μm, we rely on stacking analyses of the 70 μm data to characterize the average 70 μm properties of the X-ray sources as a function of redshift, X-ray luminosity and X-ray absorption. Using Spitzer-IRS data of the Swift-Burst Alert Telescope (BAT) sample of active galactic nuclei (AGNs), we show that the 70/24 μm flux ratio can distinguish between AGN-dominated and starburst-dominated systems out to . Among the X-ray sources detected at 70 μm, we note a large scatter in the observed 70/24 μm flux ratios, spanning almost a factor of 10 at similar redshifts, irrespective of object classification, suggesting a range of AGN:starburst ratios. From stacking analyses we find that the average observed 70/24 μm flux ratios of AGNs out to an average redshift of 1.5 are similar to AGNs with similar X-ray luminosities and absorbing column densities . Furthermore, both high-redshift and AGNs follow the same tendency towards warmer 70/24 μm colours with increasing X-ray luminosity ( LX). From analyses of the Swift-BAT sample of AGNs, we note that the 70 μm flux can be used to determine the IR (8–1000 μm) luminosities of high-redshift AGNs. We use this information to show that AGNs at high redshifts have IR to X-ray luminosity ratios that are, on average, and times higher than AGNs with similar X-ray luminosities at and ≈0, respectively. By comparison, we find that the ratios of AGNs remain largely unchanged across this same redshift interval. We explore the consequences that these results may have on the identification of distant, potentially Compton-thick AGNs using ratios. In addition, we discuss possible scenarios for the observed increase in the ratio with redshift, including changes in the dust covering factor of AGNs and/or the star formation rates of their host galaxies. Finally, we show how deep observations to be undertaken by the Herschel Space Observatory will enable us to discriminate between these proposed scenarios and also identify Compton-thick AGNs at high redshifts. [ABSTRACT FROM AUTHOR]

We review the available estimates of the masses of the compact object in ultraluminous X-ray sources (ULXs) and critically reconsider the stellar mass versus intermediate-mass black hole (BH) interpretations. BHs of several hundreds to thousands of are not required for the majority of ULXs, although they might be present in the handful of known hyperluminous objects and/or some sources showing timing features in their power density spectra. At the same time, however, stellar mass BHs may be quite a reasonable explanation for ULXs below , but they need super-Eddington accretion and some suitable dependence of the beaming factor on the accretion rate in order to account for ULXs above this (isotropic) luminosity. We investigate in detail a ‘third way’ in which a proportion of ULXs contain BHs formed in a low metallicity environment and accreting in a slightly critical regime and find that it can consistently account for the properties of bright ULXs. Surveys of ULX locations looking for a statistically meaningful relationship between ULX position, average luminosity and local metallicity will provide a definitive test of our proposal. [ABSTRACT FROM AUTHOR]

The Fractal Bubble model has been proposed as a viable cosmology that does not require dark energy to account for cosmic acceleration, but rather attributes its observational signature to the formation of structure. In this Letter, it is demonstrated that, in contrast to previous findings, this model is not a good fit to cosmological supernovae data; there is significant tension in the best-fitting parameters obtained from different samples, whereas Λcold dark matter (ΛCDM) is able to fit all data sets consistently. Furthermore, the concordance between galaxy-clustering scales and data from the cosmic microwave background is not achieved with the most recent supernova compilations. The validity of the Fractal Bubble formalism as a sound cosmological model is further challenged as it is shown that previous studies of this model achieve concordance by requiring a value for the present-day Hubble constant that is derived from supernovae data containing an arbitrary distance normalization. [ABSTRACT FROM AUTHOR]

We explore collisions between two white dwarfs as a pathway for making Type Ia supernovae (SNIa). White dwarf number densities in globular clusters allow 10–100, redshift ≲1 collisions per year, and observations by Chomiuk et al. of globular clusters in the nearby S0 galaxy NGC 7457 have detected what is likely to be a SNIa remnant. We carry out simulations of the collision between two white dwarfs at various impact parameters and mass resolutions. For impact parameters less than half the radius of the white dwarf, we find such collisions produce of56Ni, making such events potential candidates for underluminous SNIa or a new class of transients between Novae and SNIa. [ABSTRACT FROM AUTHOR]

G35.6−0.4 is an extended radio source in the Galactic plane which has previously been identified as either a supernova remnant or an H ii region. Observations from the Very Large Array Galactic Plane Survey at 1.4 GHz with a resolution of 1 arcmin allow the extent of G35.6−0.4 to be defined for the first time. Comparison with other radio survey observations show that this source has a non-thermal spectral index, with . G35.6−0.4 does not have obvious associated infrared emission, so it is identified as a Galactic supernova remnant, not an H ii region. It is in extent, showing partial limb brightening. [ABSTRACT FROM AUTHOR]

We propose a method to synthesize the inverse Compton (IC) γ-ray image of a supernova remnant starting from the radio (or hard X-ray) map and using results of the spatially resolved X-ray spectral analysis. The method is successfully applied to SN 1006. We found that synthesized IC γ-ray images of SN 1006 show morphology in nice agreement with that reported by the High Energy Stereoscopic System (HESS) collaboration. The good correlation found between the observed very high energy γ-ray and X-ray/radio appearance can be considered as evidence of the fact that the γ-ray emission of SN 1006 observed by HESS is leptonic in origin, although a hadronic origin may not be excluded. [ABSTRACT FROM AUTHOR]